This invention generally relates to heat dissipation relative to electronic circuits and more particularly to apparatus for cooling such circuits. More specifically, the invention is directed to apparatus for indirect forced-air cooling of integrated circuits (ICs) mounted on printed circuit (PC) boards.
It is widely known and recognized in the electronics industry that heat dissipation is a serious consideration in the design and operation of electronic apparatus. This is especially true for apparatus which comprise densely packaged electronic circuit components and in particular semi-conductor type circuit components such as integrated circuit components. It is known, for example, that to operate an IC at its full power capability there should be no temperature difference between the IC case housing and ambient air. This occurs, of course, only when the thermal resistance of the heat sink associated in the mounting of the IC is zero and then only when the existing thermal resistance is that which exists between the IC semi-conductor junction and the mounting case. It is not possible to make a heat sink with zero thermal resistance but the greater the ratio of junction-to-case versus case-to-ambient temperature the more closely the maximum power limit of the particular IC can be approached.
The effect of extreme high temperature on ICs will vary depending upon certain factors including the type of circuit, the packaging configuration, and the fabrication techniques used by the IC manufacturer. However, it can be generally stated that extreme high temperatures cause IC characteristics to change. For example, a temperature above that which is rated for a particular IC may cause one or more of the following to happen: increased leakage currents, increased sensitivity to noise, increased unbalance in balanced circuits, increased "switching spikes" or transient voltages in digital ICs, and/or increased chance of thermal runaway and ultimate destruction or burnout of the device.
Because of the importance of heat dissipation, various techniques are being applied to cooling of ICs and these include heat dissipation by conduction using high conductive metal heat sink mountings and/or heat dissipation by convection using cooling air that is blown over and around the ICs. In many applications where forced air may be available, it may not be used because the amount of air is limited and insufficient, or else the air is contaminated such as to make it unsuitable without elaborate filtering.
It is in accordance with one aspect of the present invention, an object to provide heat dissipation of electronic circuits by both conduction and convection heat transfer modes and without adding substantially to the volume space requirements of the apparatus utilizing such circuits.
According to another aspect of the invention it is an object to provide heat dissipation of integrated circuits in flat pack and/or dual-in-line (DIP) configurations when mounted on printed circuit (PC) boards.
In accordance with still another aspect of the invention, it is an object to provide heat dissipation in IC circuits mounted on PC boards using forced air convection cooling in conjunction with heat sink conduction cooling.